In a hydrocyclone, as the feed flowrate through the unit increases (at a fixed feed pressure), the pressure reductions from feed to overflow and from feed to underflow both increase. Thus the static pressures at the overflow and underflow of the unit both decrease. Furthermore, the static pressure at the underflow is always greater than the static pressure at the overflow. Recommended practice for many hydrocyclones states either that the ratio of overflow to feed flow (sometimes called the reject ratio) should remain constant, or that the overflow should itself remain constant, whatever the feed flow. Thus regulation of the overflow is required.
Conventionally, in order to regulate the overflow, a complex control system comprising flow and/or differential pressure measuring devices, a control valve and associated electrical and/or pneumatic supplies would be required. Such a system is expensive to install and operate and can be subject to wear, particularly in areas comprising moving parts, e.g. the valve.
It is an object of the invention to provide a method of regulating the overflow of a hydrocyclone which is effective, simple and inexpensive to construct and easy to maintain.